1. Field of the Invention
Warmed ari, oxygen, or other therapeutic gases are often required under circumstances in which bulky electrical heating apparatuses may not practically be used. For instance, accidental hypothermia (a condition in which the core body temperature drops below 35.degree. C. (95.degree. F.)) may occur as a result of accidental exposure to the cold in the outdoors, perhaps from immersion in cold water or mountain accidents. However, it can also occur in the heated indoors. Particularly susceptible persons are the elderly, infants, sportsmen and military personnel.
A traditional way of treating accidental hypothermia has been by rapid peripheral rewarming. However, this method often causes peripheral vasodilation which releases reservoirs of cooled, potentially acidic and high potassium blood to flow back to the body core, resulting in a drop in body core temperature of 0.25.degree. C.-1.6.degree. C. (0.5.degree. F.-3.degree. F.) about 30 minutes after rewarming has begun. This results in a possibility of ventricular fibrillation due to further cooling of the myocardium. Thus rapid peripheral rewarming of accidental hypothermia victims involves potential hazards which cannot be easily handled outside of a hospital environment.
Accordingly, more recent attempts have been made to rewarm hypothermic individuals by directly heating the body core rather than heating the periphery of the body. Hospital treatment of victims of hypothermia by core rewarming may involve peritoneal dialysis (introduction of warm saline solution into the abdominal cavity) or inhalation rewarming. Inhalation of warm, dry or water saturated air and/or oxygen provides small amounts of heat directly to the head, neck and thoracic core. Even the small amount of heat directly provided by this method results in very good rewarming with minimum afterdrop of core temperature without stimulating the return of cool peripheral blood which may have excessive acidity and potassium concentration.
Warm, moist air is also very useful for relieving larengectomy and tracheotomy patients, and to relieve asthmatic bronchial spasms.
As the need for such treatment often arises outside of the hospital environment and is best performed without delay, use of a device for performing such treatment which is conveniently portable is highly desirable.
2. Description of the Prior Art
As noted above, hospital treatment of hypothermia patients by means of inhalation rewarming has previously been attempted in the hospital environment. Devices for accomplishing this have generally involved large, bulky apparatus with external power sources which are portable, if at all, only in a very limited way. Exemplary of such a known device is that disclosed in U.S. Pat. No. 4,013,742 to Lang, in which a complex electrical heating system is used to heat a container of water through which a respiratory gas is bubbled. Earlier devices for heating inhalation gases, as disclosed in U.S. Pat. Nos. 540,504, 1,094,301 and 1,483,620 used such bulky and inconvenient means for heating the gases as burner flames and boiling water. More recently, as shown in U.S. Pat. No. 3,923,057 to Chalon, chemical means have been used to heat inhalation gases. However, even such means have until now required very bulky and non-portable apparatus such as that disclosed in the Chalon patent.
Some efforts have been directed in the art toward achieving a portable inhalation gas heating apparatus, as exemplified by U.S. Pat. No. 4,319,566 to Hayward et al. However, such devices as the Hayward et al device also require an external power source such as propane or battery-electric power to warm the inhalation gases, resulting in relatively high cost and limited portability.